The present disclosure relates generally to tissue cutting induced by a pulsed laser beam and the energy of the pulsed laser beam. Although specific reference is made to cutting tissue for surgery such as cataract surgery, embodiments as described herein can be used in many ways with many materials to treat one or more of many materials, such as cutting of optically transparent materials.
Cutting of materials can be done mechanically with chisels, knives, scalpels and other tools such as surgical tools. Pulsed lasers can be used to cut one or more of many materials and have been used for laser surgery to cut tissue. However, prior methods and apparatus of cutting can be less than desirable in at least some instances. For example, at least some prior methods and apparatus for cutting materials such as tissue are unsuitable due to their cost and size.
Cataract extraction is one of the most commonly performed surgical procedures in the world. A cataract is formed by opacification of the crystalline lens or its envelope (the lens capsule) of the eye. The cataract obstructs passage of light through the lens. A cataract can vary in degree from slight to complete opacity. Early in the development of an age-related cataract the power of the lens may be increased, causing near-sightedness (myopia). Gradual yellowing and opacification of the lens may reduce the perception of blue colors as those wavelengths are absorbed and scattered within the crystalline lens. Cataract formation typically progresses slowly resulting in progressive vision loss. Cataracts are potentially blinding if untreated.
A common cataract treatment involves replacing the opaque crystalline lens with an artificial intraocular lens (IOL). Presently, an estimated 15 million cataract surgeries per year are performed worldwide. The cataract treatment market is composed of various segments including intraocular lenses for implantation, viscoelastic polymers to facilitate surgical procedures, and disposable instrumentation including ultrasonic phacoemulsification tips, tubing, various knives, and forceps.
Presently, cataract surgery is typically performed using a technique termed phacoemulsification in which an ultrasonic tip with associated irrigation and aspiration ports is used to sculpt the relatively hard nucleus of the lens to facilitate removal through an opening made in the anterior lens capsule. The nucleus of the lens is contained within an outer membrane of the lens that is referred to as the lens capsule. Access to the lens nucleus can be provided by performing an anterior capsulotomy in which a small (often round) hole is formed in the anterior side of the lens capsule through which the surgeon excises the whole lens. Access to the lens can also be provided by performing a manual continuous curvilinear capsulorhexis (CCC) procedure. The lens may then be fragmented by segmenting and/or softening the lens by a femtosecond laser to aid in removal by a phacoemulsification tip. Removal of the lens with the phacoemulsification tip is then performed through a primary corneal incision, for instance. After removal of the lens nucleus, a synthetic foldable intraocular lens (IOL) can be inserted into the remaining lens capsule of the eye.
Prior methods and apparatuses to incise tissue with laser beams can be less than ideal in at least some instances. For example, femtosecond laser cutting systems are used in performing lens fragmentation. Femtosecond laser technology provides a short duration (e.g., approximately 10−13 seconds in duration) laser pulse (with energy level in the micro joule range) that can be delivered to a tightly focused point to disrupt tissue. Femtosecond lasers are well-suited for providing clean cuts in a lens through a relatively wide range of energy levels. However, the high cost and large size of femtosecond laser cutting systems prevent those systems from more widespread usage.
Infrared laser cutting systems, such as picosecond lasers, are smaller and more cost-effective relative to femtosecond laser cutting systems, but are not used for lens fragmentation. These systems provide cuts to a nucleus of the lens with energy level in the tens of micro joule range that are coarser than the cuts provided by a femtosecond laser beam. The quality of the cuts are poor and non-uniform throughout the lens, resulting in defects such as patching, incomplete cuts and excess damage from large bubbles generated by the laser. Examples of incomplete cutting includes bridging where two cut portions remain connected together, thereby complicating subsequent nucleus removal. Excess damage to the tissue creates lamella separation that crack the lens and block subsequent laser pulses. Therefore, further laser cutting is not possible once a lens is delaminated. Although infrared laser systems are attractive from a cost perspective, these performance deficiencies have prevented their use for lens fragmentation.
Thus, improved methods and systems for lens fragmentation and treating cataracts are needed. In light of the above, it would be desirable to have improved methods and apparatus of treating materials with laser beams, such as the surgical cutting of tissue to treat cataracts with cost effective surgical systems. At least some of the above deficiencies of the prior methods and apparatus are overcome by the embodiments described herein.